The major causes of metal rusting are known to be oxygen and moisture, while sodium chloride is also a known cause of rust. This is obvious from the experience that metal products are prone to corrosion near coastal areas. On the other hand, in the fields of metal members including steel sheets, bearings, steel balls and guide rails, assembly of parts by hand leads to attachment of chloride and other rust-generating factors, resulting in generation of rust. Countermeasures are therefore taken, such as cleaning removal of rust-causing factors, and the use of rust preventive oil lubricants.
Rust preventive oils commonly contain rust preventive additives (corrosion inhibitors) such as metal sulfonates, sulfonic acid amines, carboxylic acids, esters, amines and the like, but when the target of treatment is to be stored for prolonged periods, the rust preventive effect is often insufficient with rust preventive additives (corrosion inhibitors) alone. Thus, it has been proposed to use rust preventive oils containing heavy components such as waxes and petrolatum in addition to the aforementioned rust preventive additives, to further increase the rust-preventing property by thickening the rust preventive oil coating film. Such coating films block oxygen and moisture that are externally-derived causes of rust (see Patent document 1, for example).
Also, rust preventive oils containing heavy components such as waxes are associated with problems such as increased volume due to higher viscosity, impaired degreasing properties and decreased sprayability during spray coating, and therefore methods of maintaining the rust-preventing property by adding sarcosine compounds and without adding heavy components such as waxes have been proposed (see Patent document 2, for example).
For conventional metal working steps, there have been proposed cleaning/rust preventive additive compositions that serve both for cleaning and rust-prevention, in order to unify the two steps of washing and rust-prevention into a single step (see Patent document 3).